1. Field
The presently disclosed subject matter relates to a sensor for vehicle height measurement, and an apparatus for vehicle height measurement. The sensor and apparatus can be used whenever not only vehicle height but also a slant of a vehicle can be measured. The disclosed subject matter is particularly suitable for use in a headlight system including a leveling device.
2. Description of the Related Art
When a rear-wheel drive vehicle starts moving and when a vehicle having a heavy load in a trunk thereof drives, the front of the vehicle may lean slightly upwards in a direction opposite to a road. Therefore, the headlight of the vehicle may cause glare to an oncoming car because the vehicle headlight emits an upward light.
In order to prevent a vehicle headlight from causing glare, the vehicle can be configured to prevent the headlight thereof from inclining upwards from a road. To that end, the vehicle can include a leveling device to keep the headlight thereof in a horizontal position and the leveling device can include at least two vehicle height sensors to detect a lean of the vehicle. One reason for using two sensors is so that the vehicular slant can be detected by providing both a front and a rear portion of the body of the vehicle with a respective vehicle height sensor, and calculating a difference between the front and rear heights of the vehicle.
A conventional vehicle height sensor is disclosed, for example, in patent document No. 1 (Japanese Patent Application Laid Open H01-097805). FIG. 10 is an explicative diagram explaining a basic structure in the conventional vehicle height sensor that is disclosed in patent document No. 1.
The vehicle height sensor 90 includes: a light source 91 that is composed of an LED lamp 91a and a lens 91b for emitting parallel light from the light emitted from the LED lamp 91a; a shutter 92 having a slit 92 through which the parallel light passes; a light detector 93 converting the parallel light into two electrical current signals that can be divided in inverse proportion to distances from both edges 93a and 93b; and a control circuit 94 including I-V converters (current to voltage) 94a and 94b, a subtractor 94c and an adder 94d. 
Both the light source 91 and the light detector 93 are attached to a vehicular body and the shutter 92 is attached to a member that supports vehicular wheels. Therefore, while the vehicular body moves up and down, both the light source 91 and the light detector 93 also move up and down with respect to the shutter 92 which has the slit 92a. 
In this case, while both the light source 91 and the light detector 93 move up and down, the above-described two currents change and the converted voltages are output via the respective I-V converters 94a and 94b. However, when the light detector 93 receives the parallel light emitted from the light source 91, the total current of the two currents may not substantially change. Thus, while an output of the adder 94d is same, the vehicle height can be detected by measuring an output of the subtractor 94 that outputs a difference between the two converted voltages.
When a vehicular lean is detected by the vehicle height sensor 94, the two vehicle height sensors 94 are attached to a front body and a front-wheel member and a rear body and a rear-wheel member, respectively. The vehicular lean can be detected by calculating a difference between the front and rear vehicle heights output from the respective vehicle height sensors 94.
The above-referenced Patent Document is listed below and is hereby incorporated with its English abstract in its entirety.    1. Patent document No. 1: Japanese Patent Application Laid Open H01-097805
According to the above-described vehicle height sensor 90, both the light source 91 and the light detector 93 need to be attached to a vehicle body, and the shutter 92 needs to be attached to a member for supporting vehicular wheels, for example, a shock absorber, a suspension, etc. The attached member may be subject to shock from road surface variation and may be exposed to rainwater, mud, etc. Thus, it may be difficult for the vehicle height sensor 90 to include the shutter 92 attached to the member and may also be difficult to maintain a normal measuring state for measuring a vehicle height with accuracy.
In addition, the vehicle height sensor 90 may need to have a position adjusted between both the light source 91 and the light detector 93 and the shutter 92 in order to measure a vehicle height with accuracy. The adjustment may be difficult for workers to accomplish in view of the mounting location of the vehicle height sensor 90 and so on. Furthermore, it may be difficult for the sensor 90 to detect a long range of a vehicle height due to a restriction of the light detector 93 in size, and therefore it may be difficult to employ the same sensor for various vehicles.
The presently disclosed subject matter has been devised to consider the above and other problems, features and characteristics. Thus, according to an aspect of the disclosed subject matter, an embodiment of the disclosed subject matter can include a sensor for vehicle height measurement. The sensor can be employed for various vehicles from a small car to a big truck and also can be easily attached to a vehicle body because the sensor does not necessarily include a moving part. According to another aspect of the disclosed subject matter, an apparatus for vehicle height measurement can be configured to use the above-described sensor. The vehicle height measurement apparatus can measure not only vehicle height but also vehicular slant and can also be easily attached to a vehicle body along with the sensor. The vehicle height measurement apparatus can have practical uses related to a headlight system including a leveling device and the like.